Summary This proposal is to develop a novel slide-based proximity assay platform to quantify the dimerization of receptor tyrosine kinases (RTK) in tissue. Quantification of alteration of RTK dimerization upon biological stimuli or antagonist is critical to evaluate anti-cancer therapies which aim to block RTK mediated growth signaling pathway. However, there are limited methods for quantification of protein dimerization in tissue samples. Recently, we have discovered that dual emission quantum dots can be used for Fluorescence Resonance Energy Transfer (FRET) assays, in which one emission peak without FRET serves as an internal standard and the other serves as FRET emission to interact with acceptor dye. In this proposal, we will use EGFR targeted therapies in squamous cell carcinoma of the head and neck as a model system to demonstrate the feasibility of using QD-FRET for quantifying protein dimerization on tissues. Three specific aims are proposed in Phase I study: Aim 1- Prepare QD-Ab conjugates with desired affinity and specificity; Aim 2 - Develop quantification method for the QD-FRET assay; Aim 3 - Validate QD-FRET assay in human SCCHN cell lines and xenograft tissues. Completion of this Phase I project will greatly facilitate further development of the QD-FRET technology for both research and clinical settings.